In the following description of the present invention, an “electrophotographic image forming apparatus” means an apparatus which forms an image on recording medium with the use of an electrophotographic image forming method. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, and the like, for example), a facsimile machine, and the like.
A “drum supporting mechanism” means a mechanism for supporting an electrophotographic photosensitive drum employed by an electrophotographic image forming apparatus.
A “process cartridge” means a cartridge which integrally contains an electrophotographic photosensitive drum and a least one among charging means, developing means, and cleaning means, and also, is removably mountable in the main assembly of an electrophotographic image forming apparatus.
An electrophotographic image forming apparatus (which hereafter will be referred to simply as image forming apparatus), such as an electrophotographic copying machine or a laser beam printer, forms an image through the following image formation sequence: First, it uniformly charges the peripheral surface of its electrophotographic photosensitive member (which hereafter will be referred to simply as photosensitive member), and forms an electrophotographic latent image by selectively exposing the points (pixels) of the uniformly charged portion of the peripheral surface of the photosensitive drum. Then, it develops the electrostatic latent image into a visible image with the use of its developing means, and transfers the visible image, that is, image formed of toner (which hereafter may be referred to simply as developer image or toner image), onto recording medium. Then, it fixes the transferred image to the recording medium. After the transfer, the peripheral surface of the photosensitive drum is cleaned by the cleaning means: the toner remaining on the peripheral surface of the photosensitive drum after the transfer is removed by a cleaning means.
In the field of an image forming apparatus, various image forming apparatuses which employ a process cartridge system have been in practical usage. A process cartridge system integrally places a photosensitive member and one or more processing means in a cartridge so that they can be removably mountable in the main assembly of an image forming apparatus. Thus, a process cartridge system makes it possible to provide an image forming apparatus which is significantly smaller in size and easier to maintain than an image forming apparatus which does not employ a process cartridge system.
Generally, an electrophotographic photosensitive drum is supported by a drum supporting mechanism within the main assembly of an image forming apparatus. More specifically, a photosensitive drum is supported by the drum supporting mechanism, with the presence of a stopper between the photosensitive drum and the main assembly of the image forming apparatus. The stopper is attached to the inward surface of the photosensitive drum (cylindrical member). However, as means for improving an image forming apparatus in terms of the accuracy with which a photosensitive drum is rotated, it has been proposed to directly support a photosensitive drum by its peripheral surface (Japanese Laid-open Patent Application H10-149056).
There has been proposed another drum supporting mechanism (Japanese Laid-open Patent Application No. 4110128). In the case of this drum supporting mechanism, the main assembly of an image forming apparatus is provided with a pair of flat portions for supporting a photosensitive drum by the shaft portion of the photosensitive drum. The two flat portions bear the combination of the multiple forces applied to the photosensitive drum by the multiple processing means which are in contact with the photosensitive drum. This drum supporting mechanism also is intended to improve an image forming apparatus in the accuracy with which a photosensitive drum is rotated.
As for a method for coating the peripheral surface of a cylindrical component (as substrate of photosensitive drum) with photosensitive substance to form a photosensitive layer on the peripheral surface of the cylindrical component, generally, the cylindrical component is dipped into a solution of the photosensitive substance, in such a manner that the axial line of the cylindrical component remains vertical (Japanese Laid-open Patent Application 2004-94108). This method (dip-coating) is problematic in that a photosensitive drum manufactured with the use of this method is not uniform in diameter in terms of its axial direction. More specifically, the lengthwise end portion of a photosensitive drum, which was the bottom end during the manufacture is slightly different (larger) in diameter than the rest. This problem is attributable to the downward settling of the photosensitive substance which occurs after the coating of the substance, and/or the unevenness in the line of separation between the body of photosensitive substance on the peripheral surface of the cylindrical substrate, and the body of photosensitive substance in photosensitive substance container. As one of the solutions to this problem, it has been proposed to coat the peripheral surface of the cylindrical substrate beyond the area of contact between a cleaning member and the peripheral surface of a photosensitive drum, and the portion of the photosensitive drum, which is to be fitted with a seal, in terms of the axial direction of the photosensitive drum (Japanese Laid-open Patent Application H08-292642).